Many wireless local area networks (WLANs), such as those based on a communication protocol that is compatible with an IEEE 802.11 standard (which is sometimes referred to as ‘Wi-Fi’), involve contention-based distributed access systems. For example, Wi-Fi often uses single-user transmission via enhanced distributed channel access or EDCA. In particular, the WLANs are usually contention based because they typically utilize unlicensed frequency bands or spectra, which are unpredictable and are often subject to interference. The unpredictability of the interference can make coordination across multiple electronic devices (which are sometimes referred to as ‘stations’ or STAs) very challenging (especially for an unmanaged WLAN), and can result in the failure of a collision free period (CFP). However, the use of fully distributed channel access can allow a very simpler access point (AP) and a simpler network deployment (relative to a cellular network), which can make it easier and cheaper to deploy a WLAN.
Recently, contention-free multi-user transmission in uplink has been proposed in the IEEE 802.11ax standard. This approach can dramatically change how an electronic device accesses the communication medium. In particular, an electronic device can transmit without contending for the communication medium. Instead, an access point may content the communication medium for the electronic device, and may grant transmission opportunities to the electronic device using a trigger frame (which is sometimes referred to as ‘trigger-based access’ or ‘trigger-based channel access,’ e.g., uplink multi-user transmission). For example, during trigger-based uplink channel access, an access point may sense the communication medium and, as needed, perform backoff on behalf of potential uplink trigger-access-enabled electronic devices. Then, the access point may send a trigger frame with multi-user allocation information for the electronic devices. In response to the trigger frame, the electronic devices may send uplink traffic in the allocated-resource units in a synchronized manner in a multi-user transmission.
In principle, the use of trigger-based access and multi-user transmission can significantly reduce the contention by the electronic devices in the WLAN. Consequently, trigger-based access is often expected to result in improved communication performance. However, in order for the electronic devices in the WLAN to take advantage of uplink multi-user transmission, the access point usually needs to send out a trigger frame in a timely manner. If, e.g., because of congestion in the WLAN, this does not occur, then the electronic devices may only be able to use single-user transmission and the communication performance may not be improved.